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Date: Tue, 19 Apr 2011 23:47:47 +0200
From: Marcin Slusarz <marcin.slusarz@gmail.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Kyle Spaans <kspaans@uwaterloo.ca>, linux-kernel@vger.kernel.org,
        Dominik Brodowski <linux@dominikbrodowski.net>,
        Ben Skeggs <bskeggs@redhat.com>, airlied@redhat.com,
        dri-devel@lists.freedesktop.org, mjg@redhat.com,
        maciej.rutecki@gmail.com, nouveau@lists.freedesktop.org,
        Nigel Cunningham <lkml@nigelcunningham.com.au>,
        Nick Piggin <npiggin@gmail.com>
Subject: Re: 2.6.39-rc1 nouveau(?) regression (bisected)
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On Mon, Apr 18, 2011 at 01:27:10PM -0700, Linus Torvalds wrote:
> On Mon, Apr 18, 2011 at 1:02 PM, Marcin Slusarz
> <marcin.slusarz@gmail.com> wrote:
> >
> > It's some nasty corruption:
> 
> Looks like something wrote 0xffffffff to free'd memory.
> 
> Enabling DEBUG_PAGEALLOC *might* show where it happens.
> 
> >
> > [    6.523867] =============================================================================
> > [    6.523916] BUG sysfs_dir_cache: Poison overwritten
> > [    6.523949] -----------------------------------------------------------------------------
> > [    6.523950]
> > [    6.524016] INFO: 0xffff8801bb47df4c-0xffff8801bb47df4f. First byte 0xff instead of 0x6b
> > [    6.524061] INFO: Slab 0xffffea00060f7b58 objects=22 used=21 fp=0xffff8801bb47df18 flags=0x80000000000000c1
> > [    6.524110] INFO: Object 0xffff8801bb47df18 @offset=3864 fp=0x          (null)
> > [    6.524111]
> > [    6.524170] Bytes b4 0xffff8801bb47df08:  00 00 00 00 00 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a ........ZZZZZZZZ
> > [    6.524516]   Object 0xffff8801bb47df18:  6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
> > [    6.524862]   Object 0xffff8801bb47df28:  6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
> > [    6.525208]   Object 0xffff8801bb47df38:  6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
> > [    6.525556]   Object 0xffff8801bb47df48:  6b 6b 6b 6b ff ff ff ff 6b 6b 6b 6b 6b 6b 6b 6b kkkk<FF><FF><FF><FF>kkkkkkkk
> 
> So here the 0xffffffff is pretty obvious.
> 
> > and in another boot:
> >
> > [    6.704786] BUG: unable to handle kernel paging request at ffffffffbc70b058
> 
> Here it is less obvious, but it was _probably_ a regular kernel
> pointer of the type 0xffff8801bc70b058 before the high bits were
> overwritten by a 0xffffffff.
> 
> So then sysfs_refresh_inode() follows that pointer, and crashes.
> 
> Just a guess, obviously, but it looks rather likely.

Thanks. It helped a bit.
I'll send two patches in response to this message, one of which fixes this bug.

Marcin

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